High-pressure mercury vapor halide lamp having a refractory metal cylindrical auxiliary electrode

ABSTRACT

A high pressure mercury vapor halide lamp provided with an auxiliary electrode formed by a roughly continuous cylinder of a refractory metal wire spirally and coaxially surrounding and covering a greater portion of the main electrode. The advantage is low ignition voltage, especially low reignition voltage.

United States Patent Nakamura HIGH-PRESSURE MERCURY VAPOR HALIDE LAMP HAVING A REFRACTORY METAL CYLINDRICAL AUXILIARY ELECTRODE Inventor: Noboru Nakamura, S hoki-so, 397, Oaza Nishiiyozumi, Takatsuki-shi, Japan Filed: Feb. 8, 1971 Appl. No.: 113,653

Related U.S. Application Data Continuation of Ser. No. 840,812, July 10, 1969, abandoned, which is a continuation of Ser. No. 581,91 1, Sept. 26, 1966, abandoned.

U.S.Cl...' ..3l3/l98, 313/197,313/206, 313/207, 313/213, 313/229, 313/356,

Int. Cl ..I-I0lj 61/54 Field of Search ..3l3/18l, 197, 198, 206-208, 313/213, 216-217, 227, 229; 315/310, 346,

1 1 Jan. 30, 1973 [56] References Cited UNITED STATES PATENTS 1,877,716 9/1932 Claude ..315/335 2,089,325 8/1937 Aldington ..315/60 2,351,254 6/1944 Elmendorf .l315/261 2,517,126 8/1950 Macksoud ..315/336 3,234,421 2/1966 Reiling ..3 13/25 Primary Examiner-Roy Lake Assistant ExaminerDarwin R. Hostetter Attorney-Stevens, Davis, Miller & Mosher [57] ABSTRACT A high pressure mercury vapor halide lamp provided with an auxiliary electrode formed by a roughly con tinuous cylinder of a refractory metal wire spirally and coaxially surrounding and covering a greater portion of the main electrode. The advantage is low ignition voltage, especially low reignition voltage.

8 Claims, 3 Drawing Figures PATENTEDJAN 30 I973 SHEET 10F 2 HIGH-PRESSURE MERCURY VAPOR HALIDE LAMP HAVING A REFRACTORY METAL CYLINDRICAL AUXILIARY ELECTRODE CROSS-REFERENCES TO RELATED APPLICATIONS This is a continuation application of Ser. No. 840,812 filed July 10, 1969, now abandoned, which in turn is a continuation application of Ser. No. 581,9ll filed on Sept. 26, I966, now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of the ignition characteristics of a high-pressure mercury vapor lamp (hereinafter referred to as an HPMV lamp) especially those having a metal halide additive.

2. Description of the Prior Art It is well known that an HPMV lamp, in which the discharge tube is a quartz glass containing mercury and a rare gas with electrodes disposed at the bulb ends, is of a very high efficiency and of a good color rendition, when metal halide additives such as iodide or bromide of sodium, thallium, indium, etc. are added to the filling gas either separately or in combination.

Such HPMV lamps with metal halide additives, however, have disadvantages in that the ignition characteristics become worse or the ignition voltage rises, after continuous burning.

Once the HPMV lamp with metal halide additives is switched off, after a period of burning, part of the metal halide vapor in the discharge tube condenses as a film on the main electrode, which cools down more rapidly than the remaining portions of the tube. When the lamp is again switched on, the above-mentioned metal halide film obstructs the starting of arc discharge between them in electrodes, resulting in a high starting voltage.

According to the present invention, a metal wire material, having a high melting point, is used to form the auxiliary electrode. This auxiliary electrode is wound about the main cylindrical electrode in such a way as to form a roughly continuous cylindrical surface coaxially surrounding the aforesaid main electrode and covers a greater part of the main electrode in the axial direction; the clearance between the inside surface of this cylindrical auxiliary electrode and the surface of the main electrode is preferably no greater than 2 mm.

As the main electrode is surrounded by a closely adjacent auxiliary electrode, the cooling of the main electrode by convection currents of the filling gas or vapor is prevented by the auxiliary electrode. Thus the temperature drop of the main electrode, after switching off, is rather slow while the surrounding auxiliary electrode is cooled down rapidly by the convection currents of the gas and the vapor and by radiation. Part of the vapor of the metal halide in the discharge tube therefore condenses on the outside surface of the spiral-formed auxiliary electrode while the surface of the main electrode remains uncontaminated.

The ignition of the inventive lamp can be performed rapidly, without requiring the application of any high voltage as is usually necessary in conventional lamps.

The clearance between the main electrode and the auxiliary electrode is preferably less than 2 mm. as described above. If not, a metal halide film will aptly be deposited on the surface of the main electrode, resulting in the aforementioned difficulty in starting.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a side view of the HPMV lamp partially in section embodying a discharge tube with an auxiliary electrode according to the present invention.

FIG. 2 is a vertical section view of a fragment of the discharge tube and electrodes according to the present invention.

FIG. 3 is a diagram showing the starting voltage as a function of the life time of the inventive lamp compared with a conventionally constructed lamp.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Turning now to the HPMV lamp illustrated in FIG. 1, a discharge tube 1, having a main electrode 2 and an auxiliary electrode 3 on each end thereof, contains at least one metal halide such a thallium iodide, sodium iodide, or indium iodide, in addition to a small amount of mercury and a filling gas under a pressure of from 10 to 50 mm. Hg. The discharge tube 1 is enclosed in an outer bulb 4, supported by wire frames 5 and 6 which also act as lead wires and electrically connect each main electrode with a cap 7, which is fixed to the end of the outer bulb 4. Each auxiliary electrode 3 is joined to the main electrode at the opposite end of the lamp through a resistor 14 of some 50 K ohms. The space between the discharge tube 1 and the outer bulb 4 is either evacuated or filled with an inert gas. Sometimes the discharge tube is used without any outer bulb.

Referring to FIG. 2, the main electrode 2 is substantially made up of a double-wound tungsten coil 9 covered by electron-emissive material 10 and supported by a refractory-metal rod 11 coaxially penetrating the coil. The rod 11 is connected with the wire frame and lead wire 5 through a molybdenum foil 12, according to the well-known practice. The auxiliary electrode 3 is a spiral of tungsten or molybdenum shaped roughly as a continuous cylinder with each turn being very close to each adjacent turn. THe cylinder covers a greater part of the main electrode and keeps the clearance d therebetween at less that 2 mm. The auxiliary electrode 3 is connected to the main electrode 2 at the opposite end of the tube 4 through a molybdenum foil 13 and a resistor 14.

As a specific example of the above-described embodiment of the present invention, a 400 watt HPMV lamp was made, of which the discharge tube contained 3.7 mg. of thallium iodide, 2l mg. of sodium iodide and 1.3 mg. of indium iodide, in addition to 40 mg. of mercury and argon gas under a pressure of 25mm. Hg. The outer diameter of the lamp is I20 mm. and the length thereof is 285 mm. The inner diameter of the discharge tube is 18 mm. and the volume thereof is 12 cc. The main electrode was a two-layer coil of tungsten, the diameter of the tungsten wire being 0.9 mm. and the length and the outer diameter of the coil being 8 mm. and 4 mm. respectively. The auxiliary electrode was a coil of 0.5 mm. diameter tungsten wire, the inner diameter of the coil being 5.5 mm. and the length of the coil being 7 mm. The distance between the main electrodes is 50 mm.

This experimental lamp was burned with a half hour interruption for every five hours of burning, and the ignition voltage was measured. The results are shown in FIG. 3. The inventive lamp, shown by the continuous curve, and compared with a conventionally constructed lamp, shown by the dotted curve, has a lower ignition voltage which it keeps for its entire life.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description and all changes which come within the meaning and range of equivalency of claims are therefore to be embraced therein.

What is claimed:

1. A high pressure mercury vapor lamp comprising a. a discharge tube having a longitudinal axis, said tube containing mercury and at least one metal halide additive,

. a pair of cylindrical main electrodes located at opposite ends of said discharge tube, the axes of said cylindrical electrodes being coaxial with the longitudinal axis of said discharge tube, said main electrodes being covered with electron-emissive material,

. a pair of cylindrical auxiliary electrodes, one of said auxiliary electrodes surrounding each of said main electrodes, the axes of said auxiliary electrodes being coaxial with the corresponding axes of said main electrodes and the longitudinal axis of said discharge tube, the radial spacing between said auxiliary and main electrodes being no greater than 2 mm. and

means for connecting said auxiliary and main electrodes to an external power source.

2. A high pressure mercury vapor lamp as defined by claim 1 wherein said main and auxiliary electrodes are composed of refractory material.

3. A high pressure mercury vapor lamp as defined by claim 1 wherein each of said cylindrical auxiliary electrodes covers a greater part of its corresponding main cylindrical electrode.

4. A high pressure mercury vapor lamp as defined by claim 1 which further comprises a refractory metal rod located at each end of said discharge tube, said rods coaxially penetrating the cylindrical main electrode located at the corresponding end.

5. A high pressure mercury vapor lamp as defined by claim 1 wherein said metal halide additive is'selected from at least one of the group consisting of thallium iodide, sodium iodide and indium iodide.

6. A high pressure mercury vapor lamp as defined by claim 1 wherein said lamp further comprises an outer bulb surrounding said discharge tube.

7. A high pressure mercury vapor lamp as defined by claim 1 wherein said means for connecting each of said auxiliary electrodes to said power source includes a resistor.

8. A high pressure mercury vapor lamp comprising a discharge tube, a main electrode and an auxiliary electrode disposed within said dischar e tube at each end thereof, a metal halide and a smal amount of mercury filling saidtube under pressure, said discharge tube being enclosed in an outer bulb and supported therein by a frame, an outer bulb cap, lead-in wired electrically connecting said main electrode to said out bulb cap, said auxiliary electrode being a roughly continuous cylinder of refractory metal wire spirally and coaxially covering a greater portion of said main electrode, said lamp being adapted to be started by applying a voltage between the main and auxiliary electrodes and maintained by discharge between the main electrodes, the clearance between said auxiliary electrode and said main electrode being no greater than 2 mm, and each said auxiliary electrode being connected to the main electrode located at the opposite end of said discharge tube through a resistor.

' I 'UNX'HCT) STATES IATISN'I OFFICE CERTIFICATE OF CORRECTIOII Patent. No. 3,714,4 D d January 30, 1973 Invcntor(s) Noboi'u RA It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

' Please add-the following reference to a ssignee;

- l latsushita Electronics Corporation Osaka, J2PAN Please add the following priority data:

Japan ppln. No. 66191 filed September 28, 1965.

Signed and sealed this 27th day of November 1973.

(SEAL) Attest:

EDWARD M.PLETCIHER',JR. RENE D. TEGTMEYER Attesting Officer -Acting Commissioner of Patents 

1. A high pressure mercury vapor lamp comprising a. a discharge tube having a longitudinal axis, said tube containing mercury and at least one metal halide additive, b. a pair of cylindrical main electrodes located at opposite ends of said discharge tube, the axes of said cylindrical electrodes being coaxial with the longitudinal axis of said discharge tube, said main electrodes being covered with electron-emissive material, c. a pair of cylindrical auxiliary electrodes, one of said auxiliary electrodes surrounding each of said main electrodes, the axes of said auxiliary electrodes being coaxial with the corresponding axes of said main electrodes and the longitudinal axis of said discharge tube, the radial spacing between said auxiliary and main electrodes being no greater than 2 mm. and d. means for connecting said auxiliary and main electrodes to an external power source.
 2. A high pressure mercury vapor lamp as defined by claim 1 wherein said main and auxiliary electrodes are composed of refractory material.
 3. A high pressure mercury vapor lamp as defined by claim 1 wherein each of said cylindrical auxiliary electrodes covers a greater part of its corresponding main cylindrical electrode.
 4. A high pressure mercury vapor lamp as defined by claim 1 which further comprises a refractory metal rod located at each end of said discharge tube, said rods coaxially penetrating the cylindrical main electrode located at the corresponding end.
 5. A high pressure mercury vapor lamp as defined by claim 1 wherein said metal halide additive is selected from at least one of the group consisting of thallium iodide, sodium iodide and indium iodide.
 6. A high pressure mercury vapor lamp as defined by claim 1 wherein said lamp further comprises an outer bulb surrounding said discharge tube.
 7. A high pressure mercury vapor lamp as defined by claim 1 wherein said means for connecting each of said auxiliary electrodes to said power source includes a resistor. 